A known side-entry goniometer for use with a transmission electron microscope is shown in FIG. 5, where a specimen 9 is attached to the front end of a specimen holder 8. This specimen 9 is inserted between the magnetic pole pieces 22 of the objective lens. This goniometer includes a tilt mechanism for tilting the specimen holder 8 to the optical axis of the electron beam, translation mechanisms for moving the specimen in the X- and Y-directions, respectively, and a Z translation mechanism for moving the specimen substantially along the optical axis. When the specimen holder is tilted or translated by operating the tilt mechanism or some translation mechanisms, there is the possibility that the corresponding motor drives the tilt mechanism or translation mechanisms to thereby damage the specimen holder after the front end of the specimen holder 8 comes into contact with one of the magnetic pole pieces or other member. To prevent this undesirable situation, the conventional specimen-driving apparatus for use with an electron microscope is equipped with the following safety device. As an example, when a motor 30 incorporated in the Z translation mechanism is rotated to translate the specimen holder 8 along the Z-axis and the front end of the holder 8 is about to contact the magnetic pole piece 22 or the objective aperture 26, a microswitch 31 acting as a limiter is depressed to stop the rotation of the motor 30.
In the above-described conventional apparatus, the switch only serves to limit the movements of the translation mechanisms within predetermined ranges. Therefore, if the magnetic pole pieces are replaced with new ones and the gap between the pole pieces is varied, or if the specimen holder is replaced with a new one having a different thickness, then the safety device cannot adequately cope with the situation. Specifically, if the condition varies as described above, the safety device may fail to function satisfactorily. Conversely, the safety device may impede translational or tilting movement even within a region in which such movement is permitted. Hence, satisfactory observations cannot be made.
Accordingly, an apparatus free of these problems has been proposed. In particular, the contact of the specimen holder with the surroundings of the holder such as one of the magnetic pole piece or the aperture is electrically detected. The motor for driving the tilt mechanism is stopped in response to this detection. This proposed apparatus ensures that the specimen holder is brought to a stop at any desired position irrespective of variations in the conditions as described above. However, this apparatus is unable to tilt or translate the specimen into the optimum position while protecting the specimen holder and the aperture after the motor is stopped in response to the detection of the contact.